[PATCH] PHIOPT: Value-replacement check undef

[PATCH] PHIOPT: Value-replacement check undef

[Andrew Pinski]

While moving value replacement part of PHIOPT over
to use match-and-simplify, I ran into the case where
we would have an undef use that was conditional become
unconditional. This prevents that. I can't remember at this
point what the testcase was though.

Bootstrapped and tested on x86_64-linux-gnu with no regressions.

gcc/ChangeLog:

	* tree-ssa-phiopt.cc (value_replacement): Reject undef variables
	so they don't become unconditional used.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
---
 gcc/tree-ssa-phiopt.cc | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index a2bdcb5eae8..f166c3132cb 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -1146,6 +1146,13 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
   if (code != NE_EXPR && code != EQ_EXPR)
     return 0;
 
+  /* Do not make conditional undefs unconditional.  */
+  if ((TREE_CODE (arg0) == SSA_NAME
+       && ssa_name_maybe_undef_p (arg0))
+      || (TREE_CODE (arg1) == SSA_NAME
+	  && ssa_name_maybe_undef_p (arg1)))
+    return false;
+
   /* If the type says honor signed zeros we cannot do this
      optimization.  */
   if (HONOR_SIGNED_ZEROS (arg1))
-- 
2.43.0

Re: [PATCH] PHIOPT: Value-replacement check undef

[Richard Biener]

On Mon, Apr 29, 2024 at 8:52 AM Andrew Pinski <quic_apinski@quicinc.com> wrote:
>
> While moving value replacement part of PHIOPT over
> to use match-and-simplify, I ran into the case where
> we would have an undef use that was conditional become
> unconditional. This prevents that. I can't remember at this
> point what the testcase was though.
>
> Bootstrapped and tested on x86_64-linux-gnu with no regressions.

OK.

Thanks,
Richard.

> gcc/ChangeLog:
>
>         * tree-ssa-phiopt.cc (value_replacement): Reject undef variables
>         so they don't become unconditional used.
>
> Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>
> ---
>  gcc/tree-ssa-phiopt.cc | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index a2bdcb5eae8..f166c3132cb 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -1146,6 +1146,13 @@ value_replacement (basic_block cond_bb, basic_block middle_bb,
>    if (code != NE_EXPR && code != EQ_EXPR)
>      return 0;
>
> +  /* Do not make conditional undefs unconditional.  */
> +  if ((TREE_CODE (arg0) == SSA_NAME
> +       && ssa_name_maybe_undef_p (arg0))
> +      || (TREE_CODE (arg1) == SSA_NAME
> +         && ssa_name_maybe_undef_p (arg1)))
> +    return false;
> +
>    /* If the type says honor signed zeros we cannot do this
>       optimization.  */
>    if (HONOR_SIGNED_ZEROS (arg1))
> --
> 2.43.0
>